always

Header

#include <boost/hof/always.hpp>

Description

The always function returns a function object that will always return the value given to it, no matter what parameters are passed to the function object. The nullary version(i.e. always(void)) will return void. On compilers, that don’t support constexpr functions returning void, a private empty type is returned instead. This return type is specified as BOOST_HOF_ALWAYS_VOID_RETURN.

Synopsis

template<class T>
constexpr auto always(T value);

template<class T>
constexpr auto always(void);

Semantics

assert(always(x)(xs...) == x);

Requirements

T must be:

• CopyConstructible

Example

#include <boost/hof.hpp>
#include <algorithm>
#include <cassert>
using namespace boost::hof;

int main() {
    int ten = 10;
    assert( always(ten)(1,2,3,4,5) == 10 );
}

// Count all
template<class Iterator, class T>
auto count(Iterator first, Iterator last)
{
    return std::count_if(first, last, always(true));
}